At 6'4" and 270lbs, I would certainly think that you are a strong man. I would also think that a man who was 6'4" and 200lbs strong also. But you would be considered the teddy bear because you would feel nicer to cuddle with. Also, big men like yourself who have a gentle nature are considered teddy bears too. All that braun and gentleness too will make a woman...uh, swoon.
Cat is right. It is the "teddybear factor". Along with them wanting to feel safe in a way with a bigger guy. I'm not small by no means. [6'4" 270lbs] and I hear the same thing from every girl. "Your such a teddybear".
First of all, I don't think it's all that "common" to find thin fellas attracted to large ladies. Society is much harder on females in terms of shape than they are of men! Lop off the fetishists and those hunting what they perceive as an easy lay, and I'd imagine it's an equally sized "group" - gal wants teddybear kinda thing. You could have three heads and there will be someone out there that thinks that you're the best thing ever ... it's finding (and liking?) that person that proves difficult. We could all have standard, government issued bodies and still not find people we're nuts about. That's the rub!